What can we infer from Pillsbury's advice? Castling is desirable:
it whips the King out from under the central battle, and it gets a
Rook into play where lines may be opened. But it is also a move
which must be weighed against other moves. Careless, automatic
castling can waste time that could be better spent on other things,
and you can also castle from the frying pan into the fire. Below
I'll look at the whys and wherefores of castling.

Castling not at all
I show this game to all the juniors. Get your King out of the way!
And if your opponent doesn't castle, open up lines to the uncastled
King for your Rooks.Wojciechowski - Weiss (Munich)
[C15]1. e4 e6 2. d4 d5 3. Nc3 Bb4 4. Nge2 dxe4 5. a3 Bxc3+ 6.
Nxc3 f5

Castling late
Castling late runs the risk of not being able to castle at all,
because your King gets trapped in the middle. However I was very
struck watching Jon Speelman on TV many years ago, refraining from
castling to give an extra tempo for the attack. This is
characteristic of no-one so much as Petrosian.

In closed position it is difficult to open lines against the King,
and if there are no other open lines it may not be essential to
connect the Rooks.10. O-O-O b5 11. Bd3 Nb6 12. Kb1 Nc4 13. Bc1 Qb6
14. g5 Ne7 15. h4 c5 16. dxc5 Qxc5 17. Rhe1 g6 18. b3 Bg7 19. bxc4
bxc4 20. Bf1

Basman has argued that Kings are safe in the middle as long as you
don't move the central pawns. It all depends on whether your
opponent can open lines, which depends on pawn mobility.
So White must restrain the Black central pawns.15. b4 b6 16. Bd2 Kb8 17. b5 Na5 18. Na2 Nb7 19.
Nb4 Bxb4 20. axb4 Nd6